Intracranial aneurysms are the cause of subarachnoid haemorrhage in 85% of cases.
Traumatic Subarachnoid Hemorrhage.
In some patients, no source of hemorrhage can be detected.
Wang et al. in a A Systematic Review identified eight risk factors (drugs, trauma, neoplastic, vessels lesion, inflammatory lesion, blood disease, aneurysm, perimesencephalic hemorrhage) 1)